1. Field
Exemplary embodiments of the present invention relate to a fabrication method of light emitting diode and a laser lift-off apparatus for manufacturing the light emitting diode and, is more particularly, to a method for fabricating a light emitting diode using a laser lift-off apparatus including a heater.
2. Discussion
In recent years, good thermal stability and direct transition type energy band of group III-based nitrides, such as gallium nitride GaN, and aluminum nitride AN have been adopted as one of the group III-based nitride material for manufacturing light emitting diodes in the range of visible light and UV light. Typically, InGaN-based blue and green light emitting diodes have been utilized for various types of applications such as large natural color flat display panels, traffic signals, interior lightings, high density light sources, high resolution output systems, and optical communication systems.
A group III-based nitride semiconductor layer is grown on a heterogeneous substrate having a similar crystal structure to the semiconductor layer by using a metal organic chemical vapor deposition (MOCVD) or a molecular beam epitaxy (MBE) due to difficulty in growing a homogeneous substrate that permits growth of the semiconductor layer thereon. For example, a sapphire substrate with the hexagonal structure is generally used as the heterogeneous substrate. However, since sapphire is an electrical insulator, the using of the sapphire can cause to limit a structure of light emitting diodes. Thus, recent studies have focused on to grow epitaxial layers including nitride semiconductor layers on a heterogeneous substrate such as a sapphire substrate, followed by a process of lifting-off the heterogeneous substrate from the epitaxial layers in which a vertical structure type light emitting diode can be manufactured.
As for an approach of lifting-off the heterogeneous substrate, a laser lift-off technique is generally applied. According to a conventional lift-off technique, if a second substrate is a homogeneous substrate to the sapphire substrate or has a similar coefficient of thermal expansion to that of the sapphire substrate, the conventional lift-off technique, irradiating the sapphire substrate by laser beam, can be performed without significant problems. However, if the second substrate has a different coefficient of thermal expansion from that of the sapphire substrate, the conventional lift-off technique often causes cracking or fracture of epitaxial layers during separation of the sapphire substrate.
Furthermore, the difference in thermal coefficient between the second substrate and the sapphire substrate often causes bowing of the sapphire substrate after the second substrate is bonded to the epitaxial layers. The bowing of the sapphire substrate causes the laser beam to be out of focus thereby making it difficult to accurately transfer energy of the laser beam to an interface between the sapphire substrate and the epitaxial layer.
Therefore, there is a need for an approach to prevent the epitaxial layers from cracking, fracturing and bending during a process associated with a lift-off technique.